1. Field of the Disclosure
The present disclosure relates to a torque index sensor, and more particularly to a torque index sensor configured to enhance productivity with excellent economic feasibility by simplifying a magnet structure of an index sensor unit.
2. Discussion of the Related Art
In a conventional vehicle, a steering wheel connected to wheels is operated to manipulate a traveling direction. However, an operating force may decrease to make it difficult to quickly operate the vehicle, in case there is a large resistance between wheels and road surface, or there is generated an obstacle to steering operation. In order to solve the problem, a power steering system is proposed. The power steering system serves to provide a power transfer device to operation of the steering wheels, thereby reducing operating force.
In order for the power steering system to provide a force of operating the steering wheels, needs arise to measure a torque applied to a steering axis, a steering angle and an angular velocity. Apparatus of various methods are proposed for measuring torques of steering wheel. Particularly, a method for detecting a torque is largely employed for economic reasons in which a magnetic field of a magnet coupled to a steering axis is measured to detect the torque. Furthermore, a method for detecting an electromagnetic rotation is widely used to detect the steering angle and the angular velocity by employing a gear rotating along with a steering wheel and a driven gear meshed with the gear.
However, the device or system detecting the steering angle or the angular velocity suffers from disadvantages such as complicated fabrication processes, and a high probability of error occurrences from malfunction or erroneous operation, such that a method using an index sensor is employed.
A steering structure generally includes an input shaft coupled to a steering wheel, an output shaft coupled to a pinion meshed to a rack bar of wheel side, and a torsion bar connecting the input shaft to the output shaft.
In case a steering wheel is rotated, a rotational force is transmitted to the output shaft to change wheel directions responsive to operation of pinion and rack bar. In this case, if resistance is great, the input shaft is turned more to twist the torsion bar, where a twist level of torsion bar is measured by a torque sensor of magnetic field method.
An index sensor is provided for measuring angular velocity and angular acceleration by detecting rotation of a magnet rotating with the output shaft. The torque sensor and the index sensor may be modularized, and a modularized device is called a torque index sensor (TIS). That is, a torque index sensor (TIS) is an integrated device of a torque sensor for detection of steering torque in steering manipulation and an index sensor for detection of number of turns of a steering shaft, wherein these sensors are installed in a steering system of an automobile for example.
The TIS is advantageous due to structural simplicity and economic reasons, but concurrently disadvantageous due to inevitable occurrence of magnetic field interference caused by a structure in which two types of magnetization detection device are adjacently arranged. In order to solve the disadvantage, the torque sensor and the index sensor are needed to maintain a predetermined distance, such that a distance of 35 mm is generally secured to avoid occurrence of magnetic field interference.
As a result, there is generated a disadvantage of unnecessarily increasing a size of the TIS and of considering a magnetic field interference for fabricating the TIS into a compact size.
FIG. 1 is a perspective view illustrating a torque index sensor according to prior art and FIG. 2 is a perspective view illustrating essential parts of a torque sensor unit and an index unit of the torque index sensor of FIG. 1.
Referring to FIGS. 1 and 2, an input shaft that is inserted into TIS (Torque Index Sensor) from an upper side is coupled to a rotor (12) coupled to a magnet, where the rotor (12) takes the shape of a ring. An output shaft is coupled by a stator (11), where the stator (11) is discretely arranged from a periphery of the rotor (12) and includes an axially-bent vertical lug piece (13).
In a case a twist is generated to a torsion bar by a rotational difference between the input shaft coupled to the rotor (12) and the output shaft coupled to the stator (11), the rotor (12) and the stator (11) are relatively rotated, where a facing surface between the periphery of the rotor (12) and the axially-bent vertical lug piece (13) is changed to change a magnetization value, and where the changed magnetization value may be utilized to measure a torque.
A collector (14) is arranged to concentrate the magnetization value, and a torque sensor magnetic device (15) detects the magnetization value concentrated by the collector (14).
Meanwhile, an index unit is arranged at a bottom side of the torque sensor unit. The index unit includes an index magnet (31) and an index magnet device (35), where the index magnet (31) is connected to the output shaft along with the stator (11) and rotated therewith.
Although the torque sensor unit and the index unit are modularized inside a housing (22) and form an integrated configuration, each of the torque sensor unit and the index unit functions differently. That is, the torque sensor unit measures a torque change in response to change in magnetization value and sends a detection signal to a PCB (Printed Circuit Board, 21), while the index unit sends a detection signal of an amount of magnetization that is changed by the index magnet device in response to rotation of the index magnet (31).
FIG. 3 includes a cross-sectional view of an essential part of an index unit in a torque index sensor and an enlarged view of an index magnet according to prior art.
Referring to FIG. 3, an index magnet (40) is so configured as to be coupled to a periphery of an index housing (32) or to form a part of the periphery of the index housing (32). The index magnet may also approach or distance itself from an index magnetic element (35) secured to the housing (22) to generate an impulse signal.
The index magnet (40) basically includes three individual magnets for generating an impulse signal. FIG. 3 shows an enlarged view of the index magnet (40). The index magnet (40) magnetizes the index housing (32) and takes a shape of an arc to maintain magnetization amount of the index magnet device (35) at a constant level.
Meanwhile, in order to form the index magnet (40), each magnet is made to take the shape of an arc, and coupled to a contact surface (41). However, there exists a problem of naturally increasing a manufacturing cost and decreasing operational efficiency in the course of manufacturing and processing the index magnets (40). The problem results in a decreased advantage of the torque index sensor for reducing the manufacturing cost and simplifying the structure.